Endovascular therapy has long been used in treating a variety of different conditions, including control of internal bleeding, occlusion of blood vessels, and occlusion of aneurysms. A variety of different methods and occluding agents are known for use in such therapy.
Occlusion of blood vessels and aneurysms is preferably accomplished via catheter techniques which permit the selective placement of the catheter at the vascular site to be occluded. In this regard, recent advancements in catheter technology as well as in angiography now permit interventional neuroradiology including the treatment of otherwise inoperable aneurysms. Specifically, development of microcatheters and guide wires capable of providing access to vessels as small as 1 mm in diameter allows for the endovascular treatment of many aneurysms.
Endovascular treatment regimens include the use of occluding devices and occluding agents. One such class of occluding agents includes injectable fluids or suspensions, such as microfibrillar collagen, cellulose acetates, polyvinyl alcohols, and various other polymeric materials. The polymeric agents may be additionally crosslinked, sometimes in vivo, to extend the persistence of the agent at the desired vascular site. These agents are often introduced into the vasculature through the use of a balloon and/or catheter. After such introduction, materials form a substantially solid or semi-solid space-filling mass in the vasculature. There are many problems associated with the current use of the occluding agents, including leakage of the occluding agent into the patient's general circulation, expansion of the aneurysm or vessel volume during introduction of the occluding agent, and possible rupture of the aneurysm or vessel wall.
More common are occluding devices. One such device is a balloon which may be carried to the occluded vessel site at the end of the catheter, inflated with a suitable occluding agent and released from the end of the catheter. The balloon device has the advantage that it effectively fills the cross-section of the occluded vessel. However, when using intravascular balloon occlusion of aneurysms, inflation of a balloon into the aneurysm carries the risk of aneurysm rupture due to possible "overfilling" of portions of the aneurysm cavity. Balloons have also been known to leak the occluding agent into the vasculature during the period before the agent stabilizes.
Various methods for reducing the risks associated with the use of balloons and/or occluding agents have been proposed. One such method, disclosed in U.S. Pat. No. 5,795,331 to Cragg et al., involves inflating a balloon outside of the aneurysm to be occluded, thereby sealing the aneurysm off from the rest of the patient's vasculature. The balloon is positioned such that an injection port is lined up with the neck of the aneurysm to allow for the direct delivery of an occluding agent into the cavity of the aneurysm. In a preferred embodiment, a venting duct is included in the balloon to allow for evacuation of the blood contained in the aneurysm, however, incidents of overfilling and rupture have been reported using this method. For instance, see Endovascular Treatment of Experimental Aneurysms with Liquid Polymers: The Protective Potential of Stents, Szikora et al., Neurosurgery, Vol. 38, No. 2, pp. 339-47 (1996).
Despite advances in interventional radiology and endovascular therapy, there remains a need for a method for delivering an occluding agent to an aneurysm or blood vessel, and thereby occluding the aneurysm or blood vessel, which does not significantly increase the volume and/or pressure inside the aneurysm or blood vessel. Further a method is needed which reduces the likelihood of migration of the occluding agent into the vasculature of the patient.